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levels than the livestock standard at five sites. Mercury values were also higher than <br />the standard at five sites. <br />As a final note, only one exceedence of NPDES effluent criteria (Permit No. CO-0000221) <br />was observed at the outf ells associated wi [h the Seneca II Nine during 1992. On March 11, <br />1992 at NPDES 003, an oil/grease value of 12 mg/l was measured (standard is 10 mg/l). No <br />visible sheen was present. A total petroleum hydrocarbon (TPH) analysis was performed on <br />the same sample with a value of <0.2 mg/L. The differences between the oil/grease and TPH <br />values may be caused by interferences to the oil/grease analysis which will include <br />chlorophyll and certain other organic compounds as part of the oil/grease concentration. <br />Subsequent oil/grease samples collected in April and Nay were below the detection limit (1 <br />m9/L). <br />Surface Water Summary. Lower than average snowmelt runoff the past six years (see Table 2, <br />Appendix A) have generally resulted in low stream flows and NPDES discharges. Only minor <br />changes in water types were noted at sites monitored during 1992. TDS values at many <br />monitoring sites have increased, in part due to the decreased snoumelt runoff. An <br />• increase in mining areas have also contributed to increases in TDS values at the NPDES 004 <br />and 008 sites. TDS values at the NPDES 003 site have decreased slightly this year. TDS <br />values at the NPDES 002 site remain relatively constant since [his area has been <br />completely mined out. <br />References <br />American Public Health Association (Ed.). 1985. "Standard Nethods for the Examination of <br />~- Water end Wastewater", 16th Edition, Washington, D.C. <br />Brakensieh end others. 1979. "Field Nanual for Research in Agricultural Hydrology". <br />Buchanan end Sumers. 1968. "Stage Measurements at Gaging Stations". <br />Colorado Department of Health. 1986. "The Basic Standards for Ground Water-Draft Copy <br />(April)". <br />• _. 1992. "Classifications and Numeric Standards-Upper Colorado River Basin end North <br />Platte River (Planning Region 12)". <br />27 <br />